- $0 is not a creation argument after all, i.e. it is not part of "ce_argv".

I don't know... Can't we consider $0 as an "unconditional" creation argument?...

Also, it really has a different purpose. (...) $0 would be a special case either way.

I'm not sure either. To me, both $0 and $1 etc. can be used to identify an instance of an abstraction.

IMO $0 is the quick way, but has the limitation to make it (nearly) impossible to access members from the outside.

That's why it often happened to me to rename an instance [myAbs] to e.g [myAbs myabs1], then to replace $0 in [myAbs] with $1, so I can easily access [myAbs]'s members from the parent - from anywhere in fact (Actually, nowadays I tend to use as few $0 as possible).

If we could use $0 in messages, then the last operation would be more complicated (cause you couldn't simply substitute $0 with e.g $1).

So I think it's better to keep the $0/$n symmetry.

I think having a "message" object is a better idea [than $$'s one]

What I like with the $$ idea, is that it would provide a simple way to merge creation arguments with variable arguments, i.e compose a message with both the abstraction arguments and the incoming message elements.